The goal of this research proposal is to determine and examine crystal structures of three "Tra" proteins that comprise the "relaxosome", a nucleoprotein complex which is responsible for the nicking and unwinding of the plasmid DNA during conjugative DNA transfer (CDT). CDT is the process by which a conjugative plasmid is transferred between bacterial cells and is therefore an important mechanism for the horizontal transfer of genetic information amongst bacterial populations. The transfer process includes the formation of a stable mating pair between donor and recipient cells, nicking and unwinding of donor plasmid DNA, and transfer into the recipient cell. This entire process is orchestrated via a host of protein-protein and DNA-protein interactions, and while most of the players involved in this process have been identified, our understanding of the interactions between these players and links between each step of CDT remain poorly defined. Structures of the "relaxosome" proteins Tral, TraY and TraM both alone and in the presence of DNA will allow us to identify structural elements which are important for contact with plasmid DNA as well as drive subsequent biochemical and biophysical experiments aimed at understanding relaxosome protein contacts.